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/*
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 * Copyright (c) 2012, 2013 Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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package java.time.temporal;

import java.time.DateTimeException;
import java.time.Duration;
import java.time.Period;
import java.util.List;

/**
 * Framework-level interface defining an amount of time, such as
 * "6 hours", "8 days" or "2 years and 3 months".
 * <p>
 * This is the base interface type for amounts of time.
 * An amount is distinct from a date or time-of-day in that it is not tied
 * to any specific point on the time-line.
 * <p>
 * The amount can be thought of as a {@code Map} of {@link TemporalUnit} to
 * {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}.
 * A simple case might have a single unit-value pair, such as "6 hours".
 * A more complex case may have multiple unit-value pairs, such as
 * "7 years, 3 months and 5 days".
 * <p>
 * There are two common implementations.
 * {@link Period} is a date-based implementation, storing years, months and days.
 * {@link Duration} is a time-based implementation, storing seconds and nanoseconds,
 * but providing some access using other duration based units such as minutes,
 * hours and fixed 24-hour days.
 * <p>
 * This interface is a framework-level interface that should not be widely
 * used in application code. Instead, applications should create and pass
 * around instances of concrete types, such as {@code Period} and {@code Duration}.
 *
 * @implSpec This interface places no restrictions on the mutability of implementations, however
 * immutability is strongly recommended.
 * @since 1.8
 */
public interface TemporalAmount {

  /**
   * Returns the value of the requested unit.
   * The units returned from {@link #getUnits()} uniquely define the
   * value of the {@code TemporalAmount}.  A value must be returned
   * for each unit listed in {@code getUnits}.
   *
   * @param unit the {@code TemporalUnit} for which to return the value
   * @return the long value of the unit
   * @throws DateTimeException if a value for the unit cannot be obtained
   * @throws UnsupportedTemporalTypeException if the {@code unit} is not supported
   * @implSpec Implementations may declare support for units not listed by {@link #getUnits()}.
   * Typically, the implementation would define additional units as conversions for the convenience
   * of developers.
   */
  long get(TemporalUnit unit);

  /**
   * Returns the list of units uniquely defining the value of this TemporalAmount.
   * The list of {@code TemporalUnits} is defined by the implementation class.
   * The list is a snapshot of the units at the time {@code getUnits}
   * is called and is not mutable.
   * The units are ordered from longest duration to the shortest duration
   * of the unit.
   *
   * @return the List of {@code TemporalUnits}; not null
   * @implSpec The list of units completely and uniquely represents the state of the object without
   * omissions, overlaps or duplication. The units are in order from longest duration to shortest.
   */
  List<TemporalUnit> getUnits();

  /**
   * Adds to the specified temporal object.
   * <p>
   * Adds the amount to the specified temporal object using the logic
   * encapsulated in the implementing class.
   * <p>
   * There are two equivalent ways of using this method.
   * The first is to invoke this method directly.
   * The second is to use {@link Temporal#plus(TemporalAmount)}:
   * <pre>
   *   // These two lines are equivalent, but the second approach is recommended
   *   dateTime = amount.addTo(dateTime);
   *   dateTime = dateTime.plus(adder);
   * </pre>
   * It is recommended to use the second approach, {@code plus(TemporalAmount)},
   * as it is a lot clearer to read in code.
   *
   * @param temporal the temporal object to add the amount to, not null
   * @return an object of the same observable type with the addition made, not null
   * @throws DateTimeException if unable to add
   * @throws ArithmeticException if numeric overflow occurs
   * @implSpec The implementation must take the input object and add to it. The implementation
   * defines the logic of the addition and is responsible for documenting that logic. It may use any
   * method on {@code Temporal} to query the temporal object and perform the addition. The returned
   * object must have the same observable type as the input object <p> The input object must not be
   * altered. Instead, an adjusted copy of the original must be returned. This provides equivalent,
   * safe behavior for immutable and mutable temporal objects. <p> The input temporal object may be
   * in a calendar system other than ISO. Implementations may choose to document compatibility with
   * other calendar systems, or reject non-ISO temporal objects by {@link
   * TemporalQueries#chronology() querying the chronology}. <p> This method may be called from
   * multiple threads in parallel. It must be thread-safe when invoked.
   */
  Temporal addTo(Temporal temporal);

  /**
   * Subtracts this object from the specified temporal object.
   * <p>
   * Subtracts the amount from the specified temporal object using the logic
   * encapsulated in the implementing class.
   * <p>
   * There are two equivalent ways of using this method.
   * The first is to invoke this method directly.
   * The second is to use {@link Temporal#minus(TemporalAmount)}:
   * <pre>
   *   // these two lines are equivalent, but the second approach is recommended
   *   dateTime = amount.subtractFrom(dateTime);
   *   dateTime = dateTime.minus(amount);
   * </pre>
   * It is recommended to use the second approach, {@code minus(TemporalAmount)},
   * as it is a lot clearer to read in code.
   *
   * @param temporal the temporal object to subtract the amount from, not null
   * @return an object of the same observable type with the subtraction made, not null
   * @throws DateTimeException if unable to subtract
   * @throws ArithmeticException if numeric overflow occurs
   * @implSpec The implementation must take the input object and subtract from it. The
   * implementation defines the logic of the subtraction and is responsible for documenting that
   * logic. It may use any method on {@code Temporal} to query the temporal object and perform the
   * subtraction. The returned object must have the same observable type as the input object <p> The
   * input object must not be altered. Instead, an adjusted copy of the original must be returned.
   * This provides equivalent, safe behavior for immutable and mutable temporal objects. <p> The
   * input temporal object may be in a calendar system other than ISO. Implementations may choose to
   * document compatibility with other calendar systems, or reject non-ISO temporal objects by
   * {@link TemporalQueries#chronology() querying the chronology}. <p> This method may be called
   * from multiple threads in parallel. It must be thread-safe when invoked.
   */
  Temporal subtractFrom(Temporal temporal);
}
